1. Field of the Invention
The present invention relates to modified red phosphorus, a method of producing the same, a decolorized red phosphorus composition capable of suppressing coloring in dark red peculiar to red phosphorus when kneaded with a resin, modified red phosphorus used for the decolorized red phosphorus composition and a production method therefor, and a flame-retardant polymer composition using the decolorized red phosphorus composition.
2. Description of the Related Art
Red phosphorus is known to impart an excellent flame-retardant effect to synthetic resins. However, when red phosphorus is singly used, a hydrolysis reaction occurs by contact with air moisture to produce a phosphine gas, and thus red phosphorus cannot be used without modification. Therefore, modified red phosphorus stabilized by coating with an organic or inorganic material has been conventionally proposed. For example, Japanese Unexamined Patent Application Publication No. 51-105996 discloses modified red phosphorus coated with a thermosetting resin. However, the modified red phosphorus cannot be used for synthetic resins having a problem of color tones of products because the modified red phosphorus generally assumes dark red.
On the other hand, in Japanese Unexamined Patent Application Publication No. 59-195512, the applicant of the present invention discloses a method of concealing or decolorizing a dark red color peculiar to red phosphorus by using stabilized modified red phosphorus to enable free coloring of a resin which is rendered flame-retardant. The modified red phosphorus obtained by this method is red phosphorus coated with titanium oxide and an organic polymer, and concealing and decolorization of the dark red color of red phosphorus are significantly improved.
In Japanese Unexamined Patent Application Publication No. 2000-169119, the applicant also discloses a decolorized red phosphorus composition comprising modified red phosphorus and at least one inorganic pigment powder selected from oxides, hydroxides and phosphates of Zn, Al, Mg, Ti, and the like, the modified red phosphorus containing red phosphorus particles (A1) whose surfaces are coated with an inorganic pigment by reaction of a cationic water-soluble resin and an anionic surfactant or nonionic surfactant. Since the decolorized red phosphorus composition contains the modified red phosphorus and the inorganic pigment powder, a blend with a resin has an improved degree of concealing or decolorization of the dark red color of red phosphorus, as compared with a mixture of only modified red phosphorus and a resin.
However, when the decolorized red phosphorus composition disclosed in Japanese Unexamined Patent Application Publication No. 2000-169119 is sufficiently kneaded with a resin or rapidly kneaded with a resin, the inorganic pigment used as a decolorizing component diffuses into the resin from the peripheries of the modified red phosphorus particles to decrease the amount of the pigment in the peripheries of the modified red phosphorus particles. Therefore, a decolorization property deteriorates to cause the problem of leaving a light red hue in the resin after mixing.